1. Field of the Invention
The present invention relates to a method of immersing a substrate in a fine particle dispersion solution, depositing a fine particle film on a surface of the substrate, and forming an antistatic film. Particularly the invention relates to the film depositing method suitable for forming the antistatic film on the substrate whose surface has micro depressions and projections, and an image display device and a television device which are formed thereby.
2. Related Background Art
In the method of depositing various kinds of functional films on the substrate, vacuum evaporation, sputtering, a CVD method, and the like are widely known as the method of depositing the film from a gas phase. Spray coating, a dipping and pulling-up method, spin coating, electrolytic plating, electroless plating, colloidal electrodeposition, a sol-gel method, liquid-phase deposition, and the like are well known as the method of depositing the film from a liquid phase. These film depositing methods are appropriately used depending on characteristics of each method.
In the vacuum evaporation and the sputtering which are of the method of depositing the film from the gas phase, although film characteristics can be precisely controlled, directional properties exist in depositing the film. Therefore, although the vacuum evaporation and the sputtering are suitable for the film deposition on the plane-shaped substrate, it is difficult to deposit the film on the whole surface of the substrate in which the surface is not smooth. Throughput is also low because a vacuum film depositing apparatus is required. When the film is upsized, there is a problem that the apparatus becomes very expensive.
In the atmospheric pressure CVD method, although a vacuum installation is not required, generally it is necessary to heat the substrate on which the film is deposited to a high temperature, and it is necessary that the substrate has high heat-resisting properties. Because a temperature distribution of the substrate is reflected to a characteristic distribution of the film, the even temperature distribution is required in depositing the film, and the temperature distribution is difficult to control particularly in the substrate having a complicated shape.
Generally the gas phase film depositing method is suitable for production of a thin film because a film material is supplied as gas. However, because material density is low, there is the common problem that film deposition speed is relative low. On the other hand, the liquid phase film depositing method has advantages that solute density can be largely increased and the film deposition speed is large, and the throughput is high, when compared with the gas phase film depositing method. Therefore, the liquid phase film depositing method is widely used in fields in which cost reduction is required.
In the electrolytic plating and the electroless plating, the film deposition speed is high, the film can be deposited over the substrate at once at a low temperature, and the film deposition can be performed at low cost. However, in the electrolytic plating and the electroless plating, the film material is limited to a metal material in which oxidation and reduction are easy to occur.
In the electrodeposition, because pigment fine particles in colloidal dispersion are attracted to the substrate Coulomb attraction in an electrophoresis phenomenon, it is necessary that the substrate itself is conductive.
In the dipping and pulling-up method, the spin coating, and the spray coating, the film can be deposited on the substrate having a large area with an extremely simple apparatus, and these methods are the low-cost film depositing means used in various fields. A sol-gel solution, a fine particle dispersion solution, and the like can be used as the film material, and a degree of freedom is large in selecting the substrate material and the film material. However, surface tension has a large influence on these film-depositing methods when a solution layer formed on the surface of the substrate is dried, so that it is difficult that the film is evenly deposited on the substrate having a micro, complicated shape. As shown in FIG. 9A, when the film is deposited on the surface of a substrate 5 having micro depressions and projections by these methods, as shown in FIG. 9B, the solution containing the film material is attracted to the depressions on the surface of the substrate by the surface tension, and it is inevitable that films 41 are thick in the depressions and films 42 are extremely thin in the projections. As shown in a partially enlarged view of FIG. 9C, ideally it is desirable that the film has the even thickness in both the depressions and the projections. However, currently the film shown in FIG. 9C is not realized.
In the liquid phase deposition (LPD), a technology in which an oxide thin film is mainly grown on the surface of the substrate by utilizing a solution chemical reaction between film raw materials solved in the solution is actively developed in recent years, and Japanese Patent Application Laid-Open No. H06-116424 discloses the technology. In the technology, the film can be deposited across the surface at a relatively low temperature irrespective of the shape of the substrate. The technology is promising in the future. However, currently a film deposition time is long and the available substrates and film materials are restricted.
On the other hand, a phenomenon in which the fine particles are absorbed to the surface of the substrate in the solution depending on conditions is well known, and the technology which prevents the absorption of foreign materials is widely researched particularly in the field of a washing technology (see Japanese Patent Application Laid-Open Nos. H03-74845 and H09-22885).
However, the absorption of the foreign material becomes only a state in which the surface of the substrate is sparsely contaminated by the extremely small amount of foreign material, and the absorption of the foreign material can not positively be utilized as means for forming the functional film on the substrate.
The technology, in which the thick and even fine particle film is deposited on the whole area of the insulating substrate surface having the micro depressions and projections at high speed by the simple technique as shown in FIG. 9C, is not developed in the conventional technology described above.
A plane type of display device which utilizes electric field electron-emission (FED) can be cited as an example of a member which needs the above-described technology.
In the plane type of display device (FED), it is necessary to provide a withstanding atmospheric pressure support body (spacer) because the inside is in a vacuum. In the spacer, it is necessary that an even antistatic film is formed on the whole insulating substrate so that the spacer withstands high voltage and electric charges are not accumulated on the surface by electron collision (see Japanese Patent Application Laid-Open No. 2000-311605 (U.S. Pat. No. 6,485,345) and No. 2000-311609 (U.S. Pat. No. 6,600,263). In addition, in order to restrain the emission of secondary elections on the spacer surface, it has recently been studied to manufacture the spacer by forming an antistatic film on a substrate having micro depressions and projections on its surface (see Japanese Patent Application Laid-Open No. 2003-223858 (US-2003-141803A)). Therefore, the above-described film depositing methods are studied for the means for forming the antistatic film.
A problem of the invention is to realize the even resistant film deposition on the insulating substrate surface having the micro depressions and projections at high speed and at low cost, which is difficult to realize by the conventional gas phase film deposition technology and liquid phase film deposition technology, particularly the dipping and pulling-up method, the spin coating, and the spray coating. Mainly the film depositing method of the invention enables the antistatic film to be formed on the withstanding atmospheric pressure support body (spacer) having the micro depressions and projections, which is used for the plane type of display device.